Unit C Chapter 2 Section 2.3 Earthquakes

Causes of the Alaska Earthquake of 1964 This was the second largest earthquake that was ever recorded by a seismograph. It was caused by the motion of the ________________ relative to the _____ _________________. The ______ Plate is made of dense oceanic crust, so it tends to be pushed _______ the _____ dense continental crust of the _______________ Plate.

Subduction ______________ is the downturning of oceanic crust _________ another crustal plate. When this occurred, the continental crust that made up most of southern Alaska was compressed and warped by the huge pressures between these two plates. The stress caused the rock to deform or change shape by bending. Energy was stored in the deformed areas in the form of __________________. When the stress became greater than the breaking strength of the rock, a break occurred in the _________ (a crack in Earth’s crust due to the motion of one tectonic plate relative to another).

March 27, 1964 The stress was relieved on this date when the North American plate could no longer withstand the strain and suddenly moved to the southeast over the Pacific Plate. This sudden motion of the ____________ caused ____________ to be sent out. This transferred energy from the crust to other points on Earth’s surface.

Focus and Epicentre The ___________ is the region that _____ ________ along a fault during an earthquake. In the Alaskan earthquake, this breaking point was along the fault, which was a region 25km below the Earth’s surface. The __________ is the point on Earth’s surface ___________ the focus of an earthquake. In the Alaskan earthquake, Ancorage was the epicentre.

Types of Seismic Waves P-Waves A ________________ or _________ is a seismic wave that travels through rock as a series of ______________ and ______________ of particles. They are the _______ waves to arrive because they are the ___________. They are ____ frequency sound waves that can travel through solids, liquids, and gases.

Types of Seismic Waves S-Waves A _________________ or _________ is a seismic wave that travels through rock as a series of ________ and __________. They move _________ than P-waves, but they transfer ________ energy because they have a larger amplitude (maximum displacement) The rock vibrates up and down or left and right as the wave moves. This causes the rock to change shape, without changing it’s volume. Since gases do not resist a change in shape (liquids and gases flow instead), S-waves cannot pass through _________ and _________.

Longitudinal and Transverse Waves A _________________ is a wave in which the vibration of the particles is _________ to the direction the wave is travelling (P-WAVE) A _________________ is a wave in which the vibration of the particles is _____________ to the direction the wave is travelling (S-WAVE)

P-Waves, S-Waves, and Earth’s Interior Seismic waves travel at different speeds as they pass through different __________ of Earth’s interior. As _________ increases, the speed of both P-waves and S- waves increase. Sudden changes in rock ___________ cause the waves to quickly change direction. This sudden change in direction causes a region where P-waves from an earthquake cannot be detected; this region is called a ___________________. Researchers concluded that the P- wave shadow zone could be explained if Earth’s _________ were composed of different material than the mantle.

P-Waves, S-Waves, and Earth’s Interior The simplest explanation of the S-Wave shadow zone is that the outer portion of the core must be liquid, since S-waves do not move through liquids. If Earth had a uniformly solid composition from its crust to its center, both P-waves and S-waves would move in straight lines at a constant speed. Therefore, there would be no bending and no shadow zones.

Surface Waves Surface waves do not travel through the interior of Earth, but they do move along the surface of _______________. As a surface wave moves along the ground, it causes the ground to _________. Surface waves will also move the ground from ______ to ______, similar to an S-wave. Surface waves do not travel far from the ___________, and they travel slower than S-waves.

Properties of Seismic Waves

Studying Earthquakes Using Seismic Waves The ________ difference between the arrival of S- waves, as compared to P-waves, provides a method of locating the distance between the seismograph and the ____________. The farther away from the epicentre, the _________ the time difference between the arrival of the P-waves and S-waves. The time interval between the two waves can also be used with other values to determine the __________________ (a number assigned to an earthquake based upon the amount of vertical ground motion at its epicentre) of an earthquake. The Richter magnitude is useful for both categorizing and comparing earthquakes.

Tsunamis A _________ is a seismic sea wave set off by an ____________ in or near an ocean basin. The sudden movement of the sea floor that occurred as the ___________ moved under the _____________________ caused a series of enormous seismic sea waves. Most of the damage and loss of life from this earthquake was due to the resulting _____________ that moved down the Pacific coast of North America and across the Pacific Ocean.